Recorded almost exactly seven years apart, these high-class discs illuminate drummer Lou Grassi’s hard-hitting yet rhythmically sophisticated style in two advanced group contexts. At home with styles ranging from ragtime to free form, Grassi advances any project in tandem with other players, never drawing undue attention to himself.

A welcome document involving the drummer’s long-constituted – since 1995 – Po Band, Live at the Knitting Factory features flutist/saxophonist Marshall Allen, linchpin of the Sun Ra Arkestra, guesting with the 2000 version of the group. Besides Grassi, trumpeter Paul Smoker, trombonist Steve Swell and clarinettist Perry Robinson are featured along with the late bassist Wilber Morris. That same year, Grassi hooked up with three other mature players to form the Nu Band. Live in Paris, recorded in 2007, demonstrates the close cooperation which has allowed it to flourish. Although each Nu Band member is a leader in his own right – as are Po Band’s participants – the CD’s extended tracks demonstrate the group’s collegial if not musical harmony. Mercurial reedist Mark Whitecage and fiery brass man Roy Campbell have an ideal setting for their contrapuntal connections, while the drummer and solid bassist Joe Fonda – who plays in as many bands as Grassi – not only keep the music on an even keel, but solos impressively.

An example occurs on “Avanti Galoppi”, where Fonda’s taut string spanks and steady pumps unite with the drummer’s cymbal splashes and rim shots to press Whitecage’s dyspeptic clarinet squeals and Campbell’s brassy triplets further outside. In contrast, Morris’ work with the Po Band, finds the bassist and Grassi refracting textures off one another without melding. Although the two produce an ostinato upon which the horns can improvise, Morris is a more delicate stylist than Fonda. The bassist, who died in 2002, plucks cleanly and clearly, with notes audible among accelerating polyphony from four horns. More physical, and at points rhythmically vocalizing alongside his bass strokes, Fonda can both press the tempo forward chromatically and fracture the beat with quick spiccato runs or double-stopped bowing.

If these extended techniques characterize Whitecage’s style as he solos during Live in Paris, Allen, his opposite number with the PO Band, operates more like a jokey, disruptive factor. With an alto saxophone style that encompasses curlicue line twists, ghost tones and altissimo squeals, Allen creates situations where contrapuntal opposites are united by stacking reed tones with his screeching on top and Robinson’s moderato tongue fluttering on the bottom; or massing the brass and reed players to riff in measured forward motions.

Although Po Band veteran Robinson’s role is muted amid the aggressive polyphony, Swell asserts himself with little problem. Stretching the instrumental tessitura, his plunger trombone blasts and back-of-throat cries match stuttering reed jumps and rooster-like crowing from Smoker, plus bell-ringing and solid thumps from Grassi. “LoRa” is a trombone showcase as the cacophony eases so that his tailgate slurs and blustering grace notes are clearly heard.

Over the past quarter century, Grassi has been in demand to play with North American and European musicians on both continents. Hearing how group dynamics are intensified by his work, as demonstrated on these sessions, explains his appeal.